There is a conventional robot which has an end-effector with a vacuum absorption pad. This conventional robot holds an article by using an absorbing force of the vacuum absorption pad and transfers the article held by the vacuum absorption pad.
In a case that an article has a small size and a light weight, a single vacuum absorption pad may be enough to hold the article and transfer the same.
On the other hand, when an article has a large size, an end-effector may be provided with a plurality of vacuum absorption pads so that the article is absorbed by all of the vacuum absorption pads.
For example, a rectangular glass substrate used for a solar panel has a side of more than two meters so as to have a large size and a heavy weight. When transferring such a large and heavy substrate, the end-effector is provided with 15 to 20 vacuum absorption pads.
The end-effector may be provided with a floating mechanism to elastically support the vacuum absorption pad so that an article can be surely held by the vacuum absorption pad with its absorbing force.
A related art is disclosed in JP 61-214988A, JP 62-102985A, and JP 5-47898A.
In such a robot for transferring an article held by the vacuum absorption pads, when the vacuum absorption pads have become unable to achieve a normal vacuum absorbing force due to a damage or aging thereof, such deteriorated vacuum absorption pads have to be replaced with new ones.
Particularly, a glass substrate may already have a crack prior to being transferred by a transfer robot. In this situation, when a vacuum pad of the robot is pressed against the crack, the pad may be cut by the edge of the crack.
Moreover, if a glass substrate has been broken, fragments of the broken glass may attach to a floating mechanism of a vacuum absorption pad so that the back-and-forth movements of the vacuum absorption pad may be deteriorated by the fragments.
It is considered to provide each of a plurality of vacuum absorption pads with a vacuum sensor in order to check the vacuum absorbing force of each of the vacuum absorption pads. In this case, the pressure or vacuum level within each vacuum absorption pad can be detected by each vacuum sensor in the state that an article is absorbed and held by the vacuum absorption pads.
However, the vacuum sensors mounted on the vacuum absorption pads are susceptible to be damaged due to shocks which would be caused when an article is held by absorption and transferred.
Moreover, when all of the vacuum absorption pads are provided with the vacuum sensors, it is likely to unnecessarily stop the transfer robot due to erroneous operations of the vacuum sensors so that the productivity may be made even worse.
Further, dairy inspections of a plurality of vacuum absorption pads require a large amount of work load. Accordingly, it is desired to provide a monitoring apparatus that can easily and surely detect conditions of vacuum absorption pads.
Particularly, it is desired to provide a monitoring apparatus that can detect not only abnormal conditions of vacuum absorption forces of vacuum absorption pads, but also abnormal conditions of elastic supporting abilities by floating mechanisms for vacuum absorption pads.
For a transfer robot having a plurality of vacuum absorption pads on an end-effector, even when some of the vacuum absorption pads malfunction, the robot may be able to safely hold an article and transfer the same with the remaining normal vacuum absorption pads.
Therefore, it is desired to provide a monitoring apparatus that can precisely detect the point of time when the robot has become to be unable to safely transfer an article.